From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B35C21836FE; Wed, 26 Jun 2024 13:10:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719407405; cv=none; b=GaQNJ82I+V3MhmAW17eASWSJu6w86hRXWk35QEFqhbkFWkUeayD+oDM1wXIi+4EOS0sLtMjOy0dtZAnUHuSO1uaqTjkmqdIcHtvMgJ4qq5HzLt44QyOZwLtkLXPo0CBEPjqDRcfqq4r9r3qKdRlWIJG7SNX2R6RDn0RVKiigkbM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719407405; c=relaxed/simple; bh=fbyEDTduMIiV7ATd0/mO/o39aMMcYcfKWmIo8CJP4ig=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NDj2EFAQoV2jm+S1KZp4B0yZ+MWKDoMWRMEKWCQ1Y1+D9Xwulfh8iAaF0KJBLgHMfgIeSz2dcHLBb1/CCCXMoamElIjgwRmytQT3dpzRzuXekCcc28OhKDtZE35Cqjynh40bTng+2Cus4bpASBR4vUKFp/T7PKif7IeC8S4wDsw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B660F339; Wed, 26 Jun 2024 06:10:25 -0700 (PDT) Received: from [192.168.178.6] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 103273F73B; Wed, 26 Jun 2024 06:09:58 -0700 (PDT) Message-ID: <99518a43-8347-4f62-aaf6-de6ce68eca0c@arm.com> Date: Wed, 26 Jun 2024 15:09:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv2 3/3] cpuidle: teo: Don't count non-existent intercepts To: Christian Loehle , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, rafael@kernel.org Cc: vincent.guittot@linaro.org, qyousef@layalina.io, peterz@infradead.org, daniel.lezcano@linaro.org, ulf.hansson@linaro.org, anna-maria@linutronix.de, kajetan.puchalski@arm.com, lukasz.luba@arm.com References: <20240611112413.1241352-1-christian.loehle@arm.com> <20240611112413.1241352-4-christian.loehle@arm.com> From: Dietmar Eggemann Content-Language: en-US In-Reply-To: <20240611112413.1241352-4-christian.loehle@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/06/2024 13:24, Christian Loehle wrote: > When bailing out early, teo will not query the sleep length anymore > since commit 6da8f9ba5a87 ("cpuidle: teo: > Skip tick_nohz_get_sleep_length() call in some cases") with an > expected sleep_length_ns value of KTIME_MAX. > This lead to state0 accumulating lots of 'intercepts' because > the actually measured sleep length was < KTIME_MAX, so count KTIME_MAX > as a hit (we have to count them as something otherwise we are stuck) > and therefore teo taking too long to recover from intercept-heavy > scenarios. > > Fundamentally we can only do one of the two: > 1. Skip sleep_length_ns query when we think intercept is likely Isn't this what we do right now? Skip tick_nohz_get_sleep_length() for state0 and set cpu_data->sleep_length_ns to KTIME_MAX in teo_select() and then count this as an 'intercept' in teo_update(). > 2. Have accurate data if sleep_length_ns is actually intercepted when > we believe it is currently intercepted. > > This patch chooses the latter as I've found the additional time it > takes to query the sleep length to be negligible and the variants of > option 1 (count all unknowns as misses or count all unknown as hits) > had significant regressions (as misses had lots of too shallow idle > state selections and as hits had terrible performance in > intercept-heavy workloads). IMHO, you do 2 things here: (1) Set 'cpu_data->sleep_length_ns != KTIME_MAX' for '!idx && prev_intercept_idx' in teo_select(). (2) Force an update with 'cpu_data->sleep_length_ns == KTIME_MAX' to be counted as a 'hit' rather an 'intercept' in teo_update(). Can't really see how this matches the explanatory text exactly. > > Fixes: 6da8f9ba5a87 ("cpuidle: teo: Skip tick_nohz_get_sleep_length() call in some cases") > Signed-off-by: Christian Loehle > --- > drivers/cpuidle/governors/teo.c | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c > index cc7df59f488d..1e4b40474f49 100644 > --- a/drivers/cpuidle/governors/teo.c > +++ b/drivers/cpuidle/governors/teo.c > @@ -231,8 +231,13 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) > * length, this is a "hit", so update the "hits" metric for that bin. > * Otherwise, update the "intercepts" metric for the bin fallen into by > * the measured idle duration. > + * If teo_select() bailed out early, we have to count this as a hit as > + * we don't know what the true sleep length would've been. Otherwise > + * we accumulate lots of intercepts at the shallower state (especially > + * state0) even though there weren't any intercepts due to us > + * anticipating one. > */ > - if (idx_timer == idx_duration) > + if (idx_timer == idx_duration || cpu_data->sleep_length_ns == KTIME_MAX) > cpu_data->state_bins[idx_timer].hits += PULSE; > else > cpu_data->state_bins[idx_duration].intercepts += PULSE; > @@ -292,7 +297,7 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, > unsigned int hit_sum = 0; > int constraint_idx = 0; > int idx0 = 0, idx = -1; > - bool alt_intercepts, alt_recent; > + int prev_intercept_idx; > s64 duration_ns; > int i; > > @@ -370,6 +375,7 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, > * all of the deeper states a shallower idle state is likely to be a > * better choice. > */ > + prev_intercept_idx = idx; > if (2 * idx_intercept_sum > cpu_data->total - idx_hit_sum) { > int first_suitable_idx = idx; > > @@ -421,6 +427,14 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, > first_suitable_idx = i; > } > } > + if (!idx && prev_intercept_idx) { > + /* > + * We have to query the sleep length here otherwise we don't > + * know after wakeup if our guess was correct. > + */ > + duration_ns = tick_nohz_get_sleep_length(&delta_tick); > + cpu_data->sleep_length_ns = duration_ns; > + } > > /* > * If there is a latency constraint, it may be necessary to select an